The field of this invention is cooling control systems particularly for compartments of aircraft which contain heat-generating electronic equipment.
Because the electronic equipment of an aircraft generates heat during use, cooling must be provided to prevent temperatures from developing which would damage the equipment. In order to cool such electronic equipment many aircraft include a system of ducts conducting cooling air from an air pressure source through the compartment of the aircraft which houses the equipment and then to the atmosphere. The air pressure source is frequently a compressor of a turbine propulsion engine of the aircraft. However, because bleeding pressurized air from the compressor of a turbine engine decreases the power output of the engine and increases its fuel consumption, a means of matching the rate of air flow to the cooling requirements of the equipment is needed to preserve engine performance while insuring adequate equipment cooling. Further, because the ability of the cooling air to carry away heat from the equipment decreases with decreasing ambient pressure and air density as the altitude of an aircraft increases, the rate of cooling air flow must be adjusted to compensate for this decreased heat carrying capacity.
Heretofore, conventional cooling control systems have included a pneumatically actuated flow-control valve controlling the flow of cooling air to the electronics compartment and a control apparatus generating a pneumatic signal for the flow-control valve. These conventional control apparatus characteristically include a temperature-responsive valve generating the pneumatic control signal for aircraft altitudes between sea level and a predetermined altitude. The temperature sensing part of the valve is exposed to the interior of the electronics compartment. Thus, for aircraft altitudes between sea level and the predetermined altitude the temperature of the electronics compartment controls the flow-control valve and the cooling air flow. A pressure-responsive valve is also included in conventional control apparatus and is exposed to ambient air pressure to generate the pneumatic control signal for altitudes above the predetermined altitude. In order to switch control authority between the temperature-responsive valve and the pressure-responsive valve, conventional control apparatus also includes another pressure-responsive bistable valve which switches control between the first two valves at the predetermined aircraft altitude. Thus, above the predetermined aircraft altitude, the cooling air flow rate is controlled exclusively in response to aircraft altitude and not in response to the critical factor of temperature in the electronics compartment.
With such a conventional cooling control system an excess rate of cooling air flow must be provided at some aircraft altitudes which are above the predetermined altitude in order to insure against damaging over-temperature conditions of the equipment. Such an excess cooling air flow detrimentally affects the fuel consumption of the aircraft.
The most pertinent conventional control valves known to the applicant are illustrated in U.S. Pat. Nos. 2,002,057; 2,111,855; 2,353,201; 2,583,006; 2,919,711; 3,706,270; and 3,709,242.